1. Field of the Invention
The invention relates to a flow channel switching device that switches the flow channel of a fluid according to the temperature of the fluid.
2. Description of the Related Art
A valve for switching a flow channel is provided in a fluid circuit. Among various valves, a so-called thermo-valve that switches the flow channel according to the temperature of the fluid is typically used at a point at which two or more passages intersect. A thermo-valve switches a flow channel from one to the other according to the temperature of the fluid flowing through the thermo-valve. A thermo-valve is provided for, for example, a heat exchanger for an automatic transmission in a motor vehicle.
Japanese Utility Model Application Publication No. 1-98365 (hereinafter referred to as “JP-U-1-98365”) describes a transmission oil cooling apparatus that suppresses an increase in the temperature of the transmission oil by circulating the transmission oil through an oil pump, a circulation passage and an oil cooler that is provided in the circulation passage. The transmission oil cooling apparatus has a bypass passage bypassing the oil cooler. An automatic switching valve is provided at the connection portion between the bypass passage and the circulation passage. When the oil temperature is low, the automatic switching valve introduces the oil discharged from the oil pump to the bypass passage while preventing the oil from flowing into the oil cooler. When the oil temperature is high, the automatic switching valve introduces the oil discharged from the oil pump to the oil cooler while preventing the oil from flowing into the bypass passage. According to JP-U-1-98365, it is described that the transmission oil cooling apparatus can maintain the oil temperature within a desired temperature range, and can quickly increase the oil temperature when the oil temperature is low.
Meanwhile, Japanese Patent Application Publication No. 2006-64155 (hereinafter, referred to as “JP-A-2006-64155”) describes a heat exchanging system for an automatic transmission. The heat exchanging system is configured to cool the automatic transmission and the oil discharged from the automatic transmission. The heat exchanging system includes a first heat exchanger provided on the upstream side, a second heat exchanger provided the downstream side, a thermo-valve that can supply the automatic transmission with at least one of the oil that underwent the heat exchange at the first heat exchanger and the oil that underwent the heat exchange at the second heat exchanger. According to the heat exchanging system, when the oil temperature is relatively low, the thermo-valve establishes a flow channel in which the oil passed through the first heat exchanger returns to the automatic transmission while the oil passed through the second heat exchanger is interrupted to return to the automatic transmission. Conversely, when the oil temperature is relatively high, the thermo-valve establishes a flow channel in which the oil passes through both the first and second heat exchangers and then returns to the automatic transmission. According to JP-A-2006-64155, it is described that the heat exchanging system can stabilize the oil temperature.
Meanwhile, a thermo-valve is structured to switch a flow channel between a circuit communicated when the fluid temperature is low and a circuit communicated when the fluid temperature is high. When forming a fluid circuit during production, pipes and valves are first assembled together to form passages of the fluid circuit, and then the fluid circuit is filled up. However, when the fluid circuit is filled externally with the fluid at a low temperature, for example, the thermo-valve may prevent the fluid from flowing into the fluid circuit that is communicated at a high temperature.
For example, at a room temperature, the passages that circulates the fluid at a low temperature are open while the passages that circulates the fluid at a high temperature are closed. Therefore, when the fluid circuit is filled externally with the fluid at a room temperature, the fluid is prevented from flowing into the passages that are opened at a high temperature. That is, it is difficult to fill up completely the passages that are opened only at a high temperature with the fluid at a low temperature.
Therefore, for example, both the circuit that is opened at a low temperature and the circuit that is opened at a high temperature may be filled up in such a manner that after filling a portion of the fluid circuit with the fluid at a low temperature, the other portion of the fluid circuit is filled up externally with the fluid heated up to a high temperature. According to this manner, however, it takes excessively a long time to fill up the fluid circuit completely because the fluid needs to be heated.
Also, the thermo-valve may be configured to be controlled electrically such that a valve body of the thermo-valve moves from a position for low temperature to a position for high temperature even if the fluid is still at a low temperature. In this case, however, the structure of the thermo-valve becomes complicated and the cost of the thermo-valve increases.